Influence of Counteranion on the Thermal and Solution Behavior of Poly(2-(dimethylamino)ethyl methacrylate)-Based Polyelectrolytes

Abstract

Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) was synthesized and subsequently neutralized with various acids to form PDMAEMA·HCl, PDMAEMA·HBF4, and PDMAEMA·HOTf polyelectrolytes. In addition, ion exchange of the chloride anion provided polyelectrolytes with NO3−, N(CN)2−, PF6−, and Tf2N− anions. The glass transition temperature (Tg) varied significantly with anion in the order Cl− > PF6− > BF4− > NO3− > TfO− > Tf2N−. The polyelectrolytes with larger, weakly coordinated anions required less thermal energy to dissociate ionic interactions, leading to tailored thermal behavior. Solution conductivity of the water-soluble polyelectrolytes decreased in the order Cl− > NO3− > BF4− > N(CN)2− > TfO−, which was consistent with counteranion mobility. Solution rheology revealed polyelectrolyte behavior for PDMAEMA·HCl, PDMAEMA·HBF4, and PDMAEMA·HOTf. PDMAEMA·HCl underwent an electrospraying−electrospinning transition at three times the critical concentration for entanglement (Ce), which was consistent with other cationic polyelectrolytes. However, the BF4− and TfO− polyelectrolytes exhibited an onset of fiber formation at (1.4−1.8)Ce, much closer to the behavior of neutral, nonassociating polymers. Fiber diameters for all polyelectrolytes were 1−2 orders of magnitude smaller than those for neutral polymers due to increased conductivities of the electrospinning solutions.